1. Field of the Invention
The present invention relates to a robot, and particularly to an industrial robot which is provided with a main control unit for performing overall control of the robot and subcontrol units for individual control of each operating portion. This invention further relates to a robot in which the above subcontrol units have a learning function; namely, when the operating portion is first moved by an external force, its course of motion is memorized and thereafter the same motion is repeated.
2. Description of the Prior Art
At present, many and various robots are used in broad industrial fields including factories and the like, which robots serve to execute various tasks, in like manner such as a human being, as carrying an article with the hand, assembling a product, welding, painting, etc. In such robots, the working process is first programmed and simulated by digital and analog apparatus, and the robot is operated by means of a servo system. If errors happen to be detected in its operation or positioning or the like during the operating cycle, the errors are fed back to further control each operating portion so that no errors are detected any longer. Recently, a robot having a learning function has been further developed. In this robot, it is not necessary to program the operational course of the robot, but once the robot is moved by an external force, the robot itself memorizes the course of motion, and thereafter the robot can repeat the motion along the same course.
Conventionally, robots have been principally used to perform simple repetitive tasks under severe conditions such as harmful or dangerous environments, in place of human beings. However, with advancing of the function of the robot as described above, the robot is frequently used to perform tasks in cooperation with workers in the factory. Thus, some unexpected accidents may occur when a worker collides with the robot when he happens to approach the robot carelessly or when the robot moves suddenly. The robot may be also damaged in such a case. Or else, an article or a product may be broken when the robot collides with it. To prevent these accidents, various safety devices are incorporated by the conventional robots.
However, one defect in the conventional robots is that the responsive speed of a safety device is slow. That is to say, this slow response is caused by a fact that when the detecting device attached to the robot detects the approach of object, a detection signal is sent to a control unit for integrally controlling the entire robot, where the signal is discriminated and processed. Thereafter, the robot is wholly stopped or only the operating portion approaching the object is stopped in accordance with a command from the control unit. However, since the above control unit is provided with a lot of complicated programs to make the robot execute various given tasks, it takes a long time before the safety device is made operative in accordance with the signal from the detecting device.
A second defect of the conventional robot is that the detecting devices for detecting the approach to or contact with external objects have their own dead angles, which causes the above safety device not to become operative. In other words, the area where the detecting device of the robot can sense the ambient objects is ordinarily limited to only the operating range of the hands and arms, which are the operating portions of the robot and their moving directions. Consequently, there is a problem that, when workers or other objects enter into the dead angles of the detecting devices of the robot, the approach and contact sensing functions of the robot do not operate.
To prevent the above-mentioned collision or contact and to secure the safety and accurate operations, the robot has to be equipped with detecting devices without any dead angles. As precise and high technical operations are required, the robot has to be more complicated, which results in increase of dead angles. Although a number of detecting devices or sensing apparatuses may be attached to eliminate these dead angles, it is impossible to completely eliminate the dead angles due to limitation of the number of detecting devices.
A third defect is that daily maintenance is annoying as the robot becomes complicated, so that in case of failure or the like, it is difficult to find the trouble and repair it easily.
A fourth defect is that even in the robot having a learning function, an extremely large capacity control unit and high speed operation are inevitable to realize the learning function. Moreover, in the robot which is equipped with a plurality of operating portions, a further large capacity and high-speed control unit is required to make each operating portion learn the independent different operations. Thus, the robot itself has to be become extremely large and, accordingly, expensive.